1. Field of the Invention
The present invention relates to a direct fuel injection-type spark-ignition internal combustion engine.
2. Description of the Related Art
There has heretofore been known stratified charge combustion, produced by directly injecting fuel into a cylinder to form a mixture that can be favorably ignited (combustible mixture) only in the vicinity of a spark plug, at the ignition timing, to burn a lean mixture in the cylinder as a whole. To carry out the stratified charge combustion, in general, fuel is injected in the latter half of the compression stroke. It is intended that the thus injected fuel proceeds into a concave cavity formed on the top surface of the piston, is deflected toward the spark plug by the shape of the cavity, and forms a combustible mixture near the spark plug.
Japanese Unexamined Patent Publication No. 11-223127 discloses a direct fuel injection-type spark-ignition internal combustion engine in which the spark plug is arranged near the center of the upper portion of the cylinder, the fuel injector injects fuel in the shape of a fan having a relatively small thickness such that the injected fuel can vaporize easily to come into sufficient contact with high temperature and high pressure intake air in the cylinder, and the fuel injector is arranged in the periphery in the upper portion of the cylinder. The cavity extends from the center portion on the top surface of the piston to the fuel injector side of the periphery portion thereon, and has a bottom wall, a spark plug side wall, and a fuel injector side wall. The fuel injected from the oblique upper side into the cavity, impinges on the bottom wall and thereafter proceeds along the bottom wall toward the spark plug side wall. Next, the fuel is deflected toward the spark plug by the spark plug side wall.
In such a direct fuel injection-type spark-ignition internal combustion engine, if the injected fuel impinges the bottom wall of the cavity, a combustible mixture can be formed favorably in the vicinity of the spark plug. However, the injecting direction of the fuel injector is fixed on one direction, i.e., an oblique lower direction, and thus an extent between the positions of the piston in which such a fuel injection is allowed is relative narrow. Therefore, a fuel injection period is restrained and thus only a relative small amount of fuel can be injected. Accordingly, the stratified charge combustion having high fuel consumption efficiency can be carried out only in low engine load operating conditions. Besides, in high engine speed operating conditions, a period in which fuel can be injected becomes very short and thus the stratified charge combustion substantially cannot be carried out.
Therefore, an object of the present invention is to provide a direct fuel injection-type spark-ignition internal combustion engine, which can extend a period that fuel can be injected to form a combustible mixture, and which can enlarge an engine operating area in which the stratified charge combustion can be carried out to the high engine speed side and the high engine load side.
According to the present invention, there is provided a direct fuel injection-type spark-ignition internal combustion engine comprising: a fuel injector for injecting fuel as a spray in nearly the shape of a fan having a relative small thickness; a spark plug; a cavity formed on the top surface of a piston; wherein the cavity being a long and narrow groove-like shape, the spray being injected by the fuel injector such that the spray is almost parallel with the center axis of the piston, and impinging in the cavity, and the spark plug being arranged in the upper portion of the cylinder to face on the cavity.